Identifies an NSNumber object containing the duration (in seconds) of the current frame for an animated GIF image.
The frame duration can be a floating-point value. It is used when reading in, but not when writing out.
Available in Mac OS X v10.2 and later.
Declaration Syntax Version Information- Available in Monobjc Bridge: 10.6 (For Mac OS X 10.6 and later), 10.5 (For Mac OS X 10.5 and later)